Multicomponent eutectics for high temperature applications

ABSTRACT

Chromium added to form a multicomponent eutectic in Ni-Cb-Al alloys enhances oxidation resistance and hot corrosion resistance at high temperatures. Alloys of the system Ni-Cb-Al-Cr have excellent mechanical properties in addition to their good oxidation and hot corrosion resistance, particularly when cast and unidirectionally solidified.

United States Patent 1 11 1 Tarshis 1451 Oct. 23, 1973 MULTICOMPONENTEUTECTICS FOR HIGH TEMPERATURE APPLICATIONS [75] Inventor: Lemuel A.Tarshis, Latham, N.Y.

[73] Assignees General Electric Company,

Schenectady, NY.

[22] Filed: Feb. 14, 1972 [21] Appl. No.:-226,2 97

Related U.S. Application Data [63] Continuation of Ser. No. 87,907, Nov.9, 1970,

Primary Examinerl Dewayne Rutledge Attorney-Charles T. Watts [57]ABSTRACT Chromium added to form a multicomponent eutectic in Ni-Cb-Alalloys enhances oxidation resistance and hot corrosion resistance athigh temperatures. Alloys of the system Nl-Cb-Al-Cr have excellentmechanical properties in addition to their good oxidation and hotcorrosion resistance, particularly when cast and unidirectionallysolidified.

16 Claims, 5 Drawing Figures M-m-cb-cr AL 501 can as/770 A DIRECTIONAL LY 30L lO/F/EO abandoned.

52 U.S. c1. 148/32, 75 134 F, 75/135, 75/171,75/122 51 1111. C1.., C22c19/00 58 Field of Search 75/135, 171,122, 75/134 R, 134 F; 148/32 [56]References Cited UNITED STATES PATENTS 3,260,505 7/1966 Vel' Snyder75/111 1/ w 2 e a w k /00- k 01 1 a R 6 TEMP. (F)

0 4&0 e50 /2 aa /6 'oo 2b I r mswz'ao PATENTEUUCTPZS 197s 3, 767,479

In venfi'or': Lemuel A. Wars/71's,

%vv His Attorney.

MULTICOMPONENT EUTECTICS FOR HIGH TEMPERATURE APPLICATIONS This is acontinuation of application Ser. No. 87,907, filed Nov. 9, 1970, nowabandoned.

FIELD OF THE INVENTION The present invention relates to new and usefulalloys, and more particularly to alloys containing eutectic systems forhigh temperature structural applications in corrosive and oxidizingatmospheres.

BACKGROUND OF THE INVENTION Unidirectional solidification of eutecticalloys is known, for example from US. Pat. No. 3,124,452 of Kraft.Directionally solidified eutectic alloys have distinct advantages overordinary composites for longterm high temperature structuralapplications. The near-equilibrium phase transformation is brought aboutby unidirectional solidification directly from the liquid state, andusually produces structures having long-term metallurgical stability athigh temperatures even approaching that of decomposition of theeutectic. The preparation of final shapes by casting directly from themelt has the advantage of eliminating many complex processing steps.

However, heretofore, no eutectic alloy was known which provided anadequate combination of high temperature strength and oxidationresistance for practical application. Furthermore, in uses such asturbine blades, metallic bodies and articles produced from such alloysare exposed to hot corrosive conditions which include sulfurous gases aswell as oxygen, and no known eutectic alloy has provided the requisitehotcorrosion resistance, strength, long life and stability under dynamicstress conditions.

SUMMARY OF THE INVENTION It is therefore an object of the presentinvention to provide a multicomponent eutectic alloy which will havehigh temperature strength, oxidation and hotcorrosion resistance, longlife and metallurgical stability.

Another object of the invention is to provide an alloy comprising acomposition of complex intermetallic compounds, each compound containingother elements in solid solution, which alloy will be castable intoshaped, directionally solidified articles capable of exhibitingexcellent properties and long life under dynamic stress and corrosiveconditions at temperatures over 1,300F.

Other objects and advantages of the invention will become apparent fromthe following description and appended claims.

In accordance with the objects of this invention, an alloy system isprovided containing the four elements: nickel, aluminum, columbium andchromium. The eutectics of the invention contain at least two metallicphases of the group: Ni Al, Ni Cb, N iAl, Cb(Ni,

novel eutectic compositions of the invention, when unidirectionallysolidified from the melt, exhibit excellent high temperature strength aswell as resistance to hotcorrosion and oxidation.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be betterunderstood from the following description taken in conjunction with theaccompanying drawings wherein:

FIG. 1 is an electron micrograph (30,000X) of the structure of adirectionally solidified alloy of the invention, identified herein ascomposition A;

FIG. 2 is a light micrograph (2000X) of the structure of anotherdirectionally solidified alloy of the invention, identified herein ascomposition B;

FIG. 3 is a plot of ultimate tensile strength in KSI versus temperaturein degrees Fahrenheit, comparing ultimate tensile strength of one of theeutectic alloys of the invention with other known nickel-basesuper-alloys at elevated temperatures;

FIG. 4 is a plot comparing cyclic high-temperature oxidation behavior ofone of the eutectic alloys (composition A) of the invention with a knownsuperalloy; and

FIG. 5 is a plot comparing cyclic high temperature oxidation behavior ofanother of the alloys (composition B) of the invention with knownsuperalloys in the as-cast condition.

As is apparent from FIGS. 1 and 2, the microstructures of the alloys ofthe present invention comprise at least a three-phase eutectic alloy ofalternate, spaced lamellae or plates, with a third phase contained inone of the spaced lamellar phases. X-ray evidence (not shown) indicatesthat the lamellar phases are specifically oriented with respect to eachother.

For the purposes of discussion, the following designations will refer tothe various intermetallic compounds or phases of the compositions:

(B) NiAl (CSS) Chromium solid solution In FIG. 1, there is shown anelectron micrograph (30,000X) of one of the eutectic compositions(composition A) according to the invention. Three phases may be seen inthe micrograph, and appear to be (by electron micro-probe) chromiumsolid solution (CSS), epsilon phase (e), and delta phase (8). Thecomposition of the alloy of FIG. 1 is set forth below in Table I.

In FIG. 2, there is shown a light micrograph (2000X) of another alloy(composition B) according to the invention. Three phases are visible inFIG. 2, which appear to be beta phase ([3), lambda phase (A) andchromium solid solution (CS8). The composition of the alloy of FIG. 2 isset forthbelow in Table I.

Table I lists preferred compositions of two of the novel eutectics,identified below as A and B" of the present inventionv TABLE IComposition A Composition B Element Weight Atomic Element Weight AtomicNickel 58.6 58.6 Nickel 43.4 42.3 Chromium 13.9 15.7 Chromium 26.4 29.]Aluminum 5.4 11.7 Aluminum 6.6 14.1 Columbium 22.1 14.0 Columbium23.614.5 Total 100.0 100.0 Total 100.0

The weight percentages (w/o) of each of the respective elements listedin composition A and composition B may vary i 0.3 w/o.

The average chemical composition of observed eutectic morphologies wereobtained using electron microprobe and chemical techniques.

EXAMPLE 1 In order to demonstrate the remarkable properties of thealloys of the present invention, samples of each of the compositions ofTable I were cast from the melt and directionally solidified in aBridgman crystallizing apparatus, as described, for example, in thebook: Growth of Crystals by J. C. Brice, North Holland Publishing Co.,(1965) p. 125. The entire mold assembly rested on a water-cooled copperplate so that unidirectional cooling was obtained.

Unidirectionally solidified bodies of composition A, cast from the meltand directionally solidified in accordance with the foregoingdescription, were tested for high temperature strength, oxidationresistance and hot corrosion, and compared with the properties exhibitedby other known nickel-base superalloys. Table II and FIG. 3 show typicalstrength comparisons.

TABLE II ULTIMATE TENSILE (PSI) 77W Temp. Composition A" IN-100 Rene 8075F 225 to 250,000 130,000 135,000 1500F 180,000 120,000 120,000 1600F132,000 1 10,000 108,000 1700F 95,000 92,000 87,000

FIG. 3 shows a plot of ultimate tensile strength (KS1), at hightemperatures, of directionally solidified samples of composition A,contrasted with two known nickel base superalloys, lN-lOO and Rene 80.The arrow at T on the temperature scale of FIG. 3 designates theeutectic temperature of composition A. The data in Table II and thecurves of FIG. 3 indicate that the directionally solidified alloy ofcomposition A of the present invention exhibits substantially improvedtensile strength properties over known nickel base superalloys at roomtemperature and also at the technologically important temperature rangeof 1,500 to 1,700F. The compositions of the known superalloys referredto herein are given in Table V for convenience.

The alloys of the present invention exhibit especially good propertieswith respect to corrosion and oxidation at high temperatures.

INTERRUPTED OXIDATION TESTS EXAMPLE 2 Cyclic interrupted oxidation testswere conducted in static air at 1,900F for interrupted 25-hourexposures, simultanteously exposing specimens of composition A(directionally solidified) and Rene 80 (fully solution treated). Theoxidation, plotted in weight gain per unit area (mg/cm) versuscumulative time of exposure (hours) is indicated in the graph of FIG. 4and in Table III.

EXAMPLE 3 In an interrupted oxidation test similar to Example 2,specimens of composition B (directionally solidified) were exposed, instatic air at 1,900F for 25-hour exposures, simultaneously with as-castRene 80 and Rene 100. The results are shown in the graph of FIG. 5 andin Table IV.

Composition A Fully soln. treated Rene 42 mg/cm 51 mg/cm TABLE IV WeightGain per Unit Area in 500 Hp irs (l900F) I Composition B Rene 80 (as cas tl Rene 100 752550 75 mg/cm mg/cm 101 mg/em TABLE V COMPOSITIONS OFKNOWN NICKEL-BASE SU- PERALLOYS IN- Rene Rene Udimet Udimet 80 100 500700 Carbon 0.18 w/o 0.17 w/o 0.18 w/o 0.07 w/o 1O w/o Manganese 0.200.50 .20 Silicon 0.20 0.50 .30 Chromium 10.0 14.00 9.50 18.5 18.00Cobalt 15.0 9.50 15.00 18.5 1800 Aluminum 5.5 3.00 5.50 3.0 2.9 Titanium4.7 5.00 4.20 3.0 2.9 Molybdenum 3.0 4.00 3.00 4.0 4.0 Iron 0.20 1.002.0 Boron .014 0.015 0.015 006 0.01 Zirconium .06 0.03 0.06 Tungsten 4.0Vanadium 1.0 1.00 Nickel Bal. Bal. Bal. Bal. Bal.

EXAMPLE 4 To test the hot-corrosion properties of a typical alloy of theinvention, specimens were exposed at 1,800F in a small gas burner in anatmosphere containing 1 percent sulfur and 476 parts per million of seasalt, and the results were measured in average depth of corrosive attackafter 100 hours exposure. Specimens of composition A of the inventionare compared in Table VI below with similar tests conducted onsuperalloys U-50O and U-700. The corrosive attack appearance on thesurface of the specimen of the invention after exposure was perfectlyuniform, with no evidence of spike" attack, indicating no tendency toform selected regions of corrosive penetration.

TABLE VI HOT CORROSION TEST Test at l800F Small Gas Burner TestsAtmosphere: 1% S, 476 ppm Sea Salt Average Depth of Corrosion AttackAfter 100 hrs. Ex-

posure Composition A Range: 0.00097" to 0.00116" loys may also besolution heat treated and precipitation hardened, to further enhancetheir strength.

Although the disclosed alloys described herein con-' tain 3-phases, itwill be understood that eutectics of other order (e.g. quaternary etc.)containing more than three intermetallic compounds or phases may also beused, with the disclosed and other additional elements. Accordingly, afifth element modifier to the Ni-Al-Cb- Cr eutectic system may be addedto improve certain properties. For example, one or more of the elementstantalum, titanium, tungsten and molybdenum may be added. Tantalum maybe added to replace a portion of the columbium, and titanium may beadded to replace a portion of the aluminum. I

While the present invention has been described with reference toparticular embodiments and compositions thereof, it will be understoodthat numerous modifications and alterations can be made by those skilledin the art without actually departing from the scope of the invention orthe appended claims.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. A method for preparing an article having properties of high tensilestrength at elevated temperatures and good resistance, to oxidation andhot corrosion conditions, which comprises a. providing a casting alloymelt containing the elements nickel, aluminum, columbium and chromium,

b. unidirectionally solidifying from the melt a cast shape from saidalloy, the rate of said directional solidification being such as to forma eutectic microstructure consisting of at least three phases seed f me. .ar ups N s Llil NiAl, Cb(Ni AlI) Cr Cb and chromium solid solution,two of said three phases being specifically oriented with respect toeach other and the third of said phases being contained at leastpartially within one of said two specifically oriented phases.

2. A method-according to claim 1, said eutectic microstructurecontaining as phases chromium solid solution and the two intermetalliccompounds: Cr Cb and Ni Cb.

3. A method according to claim 2, said Ni Cb phase being containedpredominantly within the Cr Cb phase.

4. A method according to claim 1, said eutectic microstructurecontaining as said three phases the two intermetallic compounds: NiAland Cb(Ni ,Al and chromium solid solution.

5. A method according to claim 1 wherein said casting alloy melt is aeutectic type alloy.

6. A method according to claim 1 wherein said casting alloy melt is aninvariant eutectic type alloy.

7. A method according to claim 1 wherein the eutectic of said alloy iscomposed approximately of from 58.3 to 58.9 w/o nickel, 13.6 to 14.2 w/ochromium, 5.1 to 5.7 w/o aluminum, and 21.8 to 22.4 w/o columbium.

8. A method according to claim 1 wherein the eutectic of said alloy iscomposed approximately of from 43.1 to 43.7 w/o nickel, 26.1 to 26.7 w/ochromium, 6.3 to 6.9 w/o aluminum and 23.3 to 23.9 w/o columbium.

9. A method according to claim 1 wherein said casting alloy. melt isunidirectionally solidified from the molten condition'at a rate of lessthan 5 inches per hour.

10. The product produced by the method of claim 1.

11. The product produced by the method of claim 2.'

12. The product produced by the method of claim 3.

13. The product of claim 7 wherein the chromium of said alloy iscontained, at least in part, in the bimetallic compound Cr Cb.

14. The product of claim 7 wherein the chromium is present in theeutectic of the alloy in excess of about 7.0 weight per cent.

15. The product of claim 7 wherein the chromium is present in theeutectic in excess of about 8.0 atomic per cent.

16. A method according to claim 1, said casting alloy melt furtherincluding at least one modifier element selected from the group:tantalum,titanium, tungsten and molybdenum.

2. A method according to claim 1, said eutectic microstructurecontaining as phases chromium solid solution and the two intermetalliccompounds: Cr2Cb and Ni3Cb.
 3. A method according to claim 2, said Ni3Cbphase being contained predominantly within the Cr2Cb phase.
 4. A methodaccording to claim 1, said eutectic microstructure containing as saidthree phases the two intermetallic compounds: NiAl and Cb(Ni1 xAlx)2 andchromium solid solution.
 5. A method according to claim 1 wherein saidcasting alloy melt is a eutectic type alloy.
 6. A method according toclaim 1 wherein said casting alloy melt is an invariant eutectic typealloy.
 7. A method according to claim 1 wherein the eutectic of saidalloy is composed approximately of from 58.3 to 58.9 w/o nickel, 13.6 to14.2 w/o chromium, 5.1 to 5.7 w/o aluminum, and 21.8 to 22.4 w/ocolumbium.
 8. A method according to claim 1 wherein the eutectic of saidalloy is composed approximately of from 43.1 to 43.7 w/o nickel, 26.1 to26.7 w/o chromium, 6.3 to 6.9 w/o aluminum and 23.3 to 23.9 w/ocolumbium.
 9. A method according to claim 1 wherein said casting alloymelt is unidirectionally solidified from the molten condition at a rateof less than 5 inches per hour.
 10. The product produced by the methodof claim
 1. 11. The product produced by the method of claim
 2. 12. Theproduct produced by the method of claim
 3. 13. The product of claim 7wherein the chromium of said alloy is contained, at least in part, inthe bimetallic compound Cr2Cb.
 14. The product of claim 7 wherein thechromium is present in the eutectic of the alloy in excess of about 7.0weight per cent.
 15. The product of claim 7 wherein the chromium ispresent in the eutectic in excess of about 8.0 atomic per cent.
 16. Amethod according to claim 1, said casting alloy melt further includingat least one modifier element selected from the group: tantalum,titanium, tungsten and molybdenum.